This invention relates in general to the field of frequency-modulated (FM) continuous-wave (CW) systems, and, more particularly, to bandpass filter demodulation for FM-CW harmonic processing radar.
In small caliber air target (SCAT) radar, for example, bandpass filtering and demodulation are key steps in the fuzing process which determines when to fire a small caliber munition. The SCAT radar system, housed in the fuze of the small caliber munition, makes the determination to issue the fire command based on an analysis comparing a radar signal reflected from the target to the radar signal transmitted by the SCAT radar system. The reflected signal is detected and mixed with the transmitted signal to produce a difference signal. The difference signal can be analyzed for Doppler shift and other information which forms the input for a fuzing algorithm to analyze. Based on predetermined criteria, the fuzing algorithm determines whether to issue the fire command. The bandpass and demodulation functions, operating on the difference signal, produce the input signal to the fuzing algorithm.
Bandpass filter demodulation can be achieved in discrete implementations using active or passive filtering and demodulation or in a non-precision integrated circuit (IC) analog implementation requiring external components. Neither of these conventional methods provides a very workable approach for bandpass filter demodulation in SCAT radar, however. Discrete implementation, requiring external parts, is not well suited to the very limited packaging volume available in small caliber fuzes. Similarly, the need for a fairly selective bandpass filter at 500 kiloHertz (kHz) and a multi-pole Doppler filter with a 50 kHz bandwidth for SCAT radar places severe demands on the external parts count or requires the use of "on chip" resistors and capacitors which are very low-precision components producing excessive filter performance variability.
Thus, a method and device for permitting a bandpass filter function and low-pass Doppler filter function to be realized in a single functional element also performing demodulation are highly desirable. Such a bandpass filter demodulator should minimize the need for external parts, reduce the circuitry required for the filtering and demodulation over discrete implementations and non-precision IC analog implementations and produce a filtering function which automatically tracks variations in system timing.